The present invention relates to a method and apparatus for damping mechanical oscillations of shafts of a machine tool, manufacturing machine or robot by providing feedback elements that apply a negative feedback output signal from each feedback element to the desired rotational speed value of a speed controller for a motor driving the shaft.
Modern machine tools, manufacturing machines or robots frequently produce undesired oscillations, particularly about the shafts and in particular the NC-shafts (numerical-control shafts) of the machine. It is to be understood by persons skilled in the art that the term “machine” is used here in a generic sense and the principles described in the following description with respect to machine are equally applicable to robots. The oscillations are caused by poorly damped mechanical resonances in the mechanical system of the machine. As a result, the speed of the shaft is increased above or reduced below the point where the undesired resonance occurs. Such resonance produces undesirable chatter marks that mechanically strain the machine, and leads to a decrease in the processing accuracy. As a rule, the mechanical system of the machine has several areas of resonance, which have respective limited frequency ranges.
In a conventional drive controller, a superordinated position-control circuit provides a desired motor speed to a subordinated speed controller for rotation of the machine shafts. In the event a respective gain is selected for the speed controller, the mechanical resonances of the mechanical system of the machine are clearly noticeable in the form of drops and increases in the amplitude excursions of the reference frequency response in the speed control circuit. Only a very limited damping of these resonance oscillations is possible with the position control means available. This conventional approach is unsuitable for implementing an effective damping of the oscillations caused by mechanical resonance. The result is inadequate machine dynamics and chatter marks, as well as the gain in the position controller being limited to just a small adjustable range.
German Pat. No. DE 196 20 439 C2 discloses a method of damping mechanical oscillations in machine tools and robots, saw-tooth oscillations in particular, as well as rotational oscillations. Two control variables are determined by two acceleration detectors and fed back via the controller to a drive controller as a desired value.
It would therefore be desirable and advantageous to provide an improved method and apparatus of damping mechanical oscillations, to obviate prior art shortcomings and to exhibit limited oscillation frequency ranges for shafts of machine tools, manufacturing machines or robots, while being simple and cost-efficient.